✨➖📝 cli, vanth, meta, flake: Simplify dependencies, add meta crate, and improve docs

- Removed dependencies `sqlx` and `bevy_app` to simplify the project.
- Added new crate `vanth_meta` for generating example SVGs.
- Updated CLI tests to use `assert_cmd` for better test assertions.
- Enhanced README with comprehensive library and CLI usage documentation.
- Modified `Store::write` in `vanth` crate to return the content hash.
- Set `checkPhase` to empty in Nix flake configuration.

flake.nix

@@ -59,6 +59,7 @@
                         strictDeps = true;
                         nativeBuildInputs = packages;
                         buildInputs = packages;
+                        checkPhase = "";
 
                         CARGO_BUILD_INCREMENTAL = "false";
                         RUST_BACKTRACE = "1";